Effects of bedrock water availability on growth and ecophysiology of Douglas-fir (Pseudotsuga menziesii) and Pacific Madrone (Arbutus menziesii) in southwest Oregon PublicDeposited

Descriptions

Effects of bedrock water availability on growth and ecophysiology of Douglas-fir [Pseudotsuga TnenzieSii (Mirb.) Franco) and Pacific madrone (Arbutus inenziesii Pursh) were studied in southwest Oregon in 1990. Bedrock physical features, including bulk density, water holding capacity, and available water capacity, were examined at
different depths from 1.0 to 3.0 in. Bulk density increased with an increase of soil/rock depth, whereas water holding capacity and available water capacity
decreased with an increase of bulk density, i.e., increase of depth. The soil/rock water depletion patterns for three treatments, no-, medium-, and high-madrone density, was
measured by using a neutron-probe soil water meter from March to September. The cumulative water used by both Douglas-fir and madrone was calculated. There was no
significant difference on total water used from June to September among three treatments. However, species in high madrone density plots depleted more water in June
than others, whereas in plots of 10-year-old Douglas-fir only, rock water depletion was the least. Medium madrone densities were depleted to an intermediate degree. Douglas-fir in no-madrone plots did not use the soil/rock water as rapidly as the rate of depletion in high- and medium-madrone density plots. Root distributions for both madrone and mature Douglas-fir were measured. Madrone roots can penetrate as
deep as 3.5 m or even deeper, whereas root systems of old growth Douglas-fir can only penetrate down to 2.0 to 2.5 m in bedrock.
Plant xylem pressure potentials in predawn and midday for both Douglas-fir and madrone were measured from July to September. Madrone had lower plant xylem pressure
potentials both in predawn and midday than those of Douglas-fir; these may be adaptive characteristics for madrone in this area.
Growth of 10-year-old Douglas-fir and madrone was monitored in September, 1990, including height and basal diameter. Basal diameter growth of Douglas-fir was affected by madrone density. Douglas-fir height growth
in high madrone density plots was significantly less than those in medium madrone density plots and Douglas-fir
only plots.